Alpha-methylene-gamma-butyrolactone and methyl alpha-methylene-gamma-butyrolactone are useful monomers in the preparation of both homopolymers and copolymers. In addition, the alpha-methylene-gamma-butyrolactone group is an important structural feature of many sesquiterpenes of biological importance.
U.S. Pat. No. 6,313,318 describes a method for converting certain starting lactones to alpha-methylene substituted lactones using a so-called basic catalyst that is made by treating silica with an inorganic salt of Ba, Mg, K, Cd, Rb, Na, Li, Sr, and La. A problem with silica-based catalysts is that they are hydrothermally unstable under reaction conditions involving temperatures above about 250° C. In addition, regeneration cycles involving air produce water at high temperature, and the water can change the porosity and activity of the catalyst.
The prior art in this area involves the use of supported catalysts on silica, which are known to be hydrothermally unstable (see for instance, WO9952628A1). Under reaction conditions, or after repeated regeneration cycles, a hydrothermally unstable material will show catalytic performance that will deteriorate with time.
Hydrotalcites are layered, double hydroxides of general formula(M2+1-xM3+x(OH)2)(An−x/n).yH2Owherein the M2+ ions can be a variety of divalent cations (e.g., Mg, Ni, Zn, Co, Fe, Cu) and the M3+ ions can be Al, Fe or Cr. Some hydrotalcites are described by V. K. Diez, C. R. Apesteguia, and J. I. DiCosimo (Latin American Applied Research, 33, 79-86 (2003)) and N. N. Das and S. C. Srivastava (Bull. Mater. Sci. 25, (4), 283-289 (2002)).
Although hydrotalcites are known, and the thermal decomposition of them is known to produce materials that are catalytic for some purposes, their thermal decomposition to produce catalysts for lactone methylenation has not been described. The catalytic activity of such materials for lactone conversion reactions cannot be predicted because of the unpredictable nature of catalysis in general.
It would be advantageous, however, to have a lactone methylenation catalyst that is hydrothermally stable at high temperatures and whose activity does not decay with time on stream (TOS) or after several high temperature oxidizing regenerations.